It is often necessary to apply localized heat in a very precise manner to heat portions of articles during the manufacture thereof. In one specific instance, paper cups or other containers have polycoated interior surfaces which must be heated rapidly and accurately in order to provide high quality, leak-proof seams during manufacture of the containers.
Various known means for heating paper cups, containers or other coated paper webs include direct flame heaters, indirect flame heaters, and other types of heaters which utilize secondary air to mix with and assist in flame combustion. Representative prior U.S. patent documents including U.S. Pat. Nos. 4,549,866; 4,042,317; and 3,977,306.
By way of background, a container blank is typically folded to form an axial side seam and essentially simultaneously mated with a flanged bottom disk. The side seam is typically a simple overlap of the blank edges, while the bottom seam typically involves rolling an extended side wall portion together with the disk flange to form an annular rolled seam about the bottom of the cup or container. For an effective bottom seam, the disk flange and the entire extended side wall portion must be sufficiently and uniformly heated. The assembly and sealing of the cups is typically performed as the cup blank is fed through a series of stations with the aid of a turntable indexed to the individual stations.
In one gas fired burner designed specifically to seal the bottom seam between a cup side wall and a cup bottom, a burner head is fitted to one end of a gas/air supply pipe, with the burner head having an outer diameter sufficiently small so that the burner head readily fits within the interior of the extended cup side wall at a location adjacent the bottom disk. Typically, such burner heads have a plurality of nozzles located about the periphery of the remote end of the head, as well as a pilot flame aperture adjacent the nozzles, with a flame ignitor/sensor device located in proximity to the pilot flame. The ignitor/sensor is associated with a control system which is effective to shut down the bottom burner (as well as other side seam burners) and the can forming apparatus if the pilot flame is out.
This arrangement has proved problematic, however, since the burner head diameter is necessarily kept small so that the pilot flame and flame ignitor/sensor device will also fit within the confines of the cup side wall. As a result, the flame nozzles are spaced farther away from the bottom seam than desired, and portions of the extended side wall are often insufficiently heated.
In accordance with this invention, the forward end of the burner head, and particularly the combustion chamber portion of the head, has been extended in length so that the pilot flame and flame sensor can be located axially behind, i.e., outside the cup bottom. At the same time, this has allowed an increase in the burner head outer diameter, such that the nozzles are moved closer to the seam. In addition, because the extended portion of the burner head includes the combustion chamber, that portion of the burner head which glows red extends throughout the entire axial length of the extended cup side wall portion, resulting in uniform heat distribution to the entire extended cup wall portion.
Another feature of the invention relates to the burner head being axially split into two sections, with the annular parting line passing through the pilot flame hole. With this arrangement, the rearward sleeve portion of the burner head can be retracted to form an annular pilot flame ring or gap. This facilitates ignition and rapid heat up, ensuring a stable flame. After a predetermined period of time, the rearward sleeve portion is moved forward to close the annular gap, leaving an otherwise conventional pilot flame aperture to perform the usual pilot flame function in cooperation with the flame sensor probe.
Accordingly, in its broader aspects, the present invention relates to a cup sealing system comprising a cup former and a plurality of burners for sealing different portions of the cup and related cup bottom, and specifically to an improvement wherein one of the plurality of burners is arranged to have a pilot flame at an orifice of the burner axially adjacent one portion of the cup; a flame sensor positioned radially adjacent the orifice to sense the presence or absence of the pilot flame; and wherein a combustion chamber of the burner extends from a forward edge of the burner to a location axially beyond the container side wall to thereby achieve uniform heating of the lower end of the cup.
In another aspect, the invention relates to a cup sealing system comprising a cup former and a plurality of burners for sealing different portions of the cup and related cup bottom wherein a cup side wall blank is mated with a bottom disk, with one portion of the side wall extending beyond the bottom disk; an improvement wherein one of the plurality of burners includes a burner head with a plurality of circumferentially arranged flame nozzles and a pilot flame aperture, the pilot flame aperture adapted to be located axially adjacent the one portion of the cup side wall; a flame ignitor/sensor positioned adjacent the flame aperture; and wherein a combustion chamber of the burner extends from a forward edge of the burner at the flame nozzles to a location axially beyond the container side wall to thereby achieve uniform heating of the extended portion of the cup side wall.
Other features of the invention will become apparent from the detailed description which follows.